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X ray questions:What material is suitable in windows for hard X-rays?

  1. Dec 8, 2011 #1
    What material is suitable in windows for hard X-rays?

    What material would you choose as reflective coating of X-rays mirrors for radiation at 200 eV? Why?
     
  2. jcsd
  3. Feb 24, 2012 #2
    Hmm, 200 eV is very very soft. The only window you can use for that is a free-stainding SiN membrane one a Si frame (substrate with a small window etched into it). These are commercially available, up to maybe a few window mm size.

    A window is always a compromise of thickness and the material's absorption length. The latter depends on Z. Generally speaking you want Z as low as you can get, but the material has to withstand possible radiation damage.

    For x-rays above 3.5keV or so you can use Beryllium (Z= 4 for large pieces) or CVD diamond (Z=6 for smaller pieces). For hard x-rays above 20keV or so you can use Al, plastics or even Si wafers.

    For 200 eV I would use a naked Si mirror without any coating. The critical angle at 200 eV is large enough, and Si you can get in excellent quality.

    Check out the Center for X-Ray Optics. There you can calculate transmission and reflectivity of softish X-rays.

    http://henke.lbl.gov/optical_constants/
     
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